Titration of Acetic Acid in Vinegar

 

Titration of Acetic Acid in Vinegar

Titration is a quantitative analysis of an unknown solution by a standard one to determine its concentration and the amount used in the reaction. A measured volume of the analyte is reacted with a fixed volume of a solution whose concentration is known. In most titrations, an indicator such as phenolphthalein is used to determine the reaction’s endpoint. This experiment determines the concentration of acetic acid in a solution of vinegar by titrating a solution of acetic acid against a low concentration of sodium hydroxide solution.

Procedure

• Clamp a burette in a stand and place a 100 mL clean beaker below the burette.
• Add 10 mL of 0.50 M of sodium hydroxide solution into the burette.
• Rinse the beaker with distilled water. Using a graduated measuring cylinder, measure 5 mL of vinegar into the 100 mL beaker. Add two drops of phenolphthalein indicator and shake.
• Titrate the mixture with sodium hydroxide solution until a permanent pink color indicating the endpoint is observed. Record the volume of sodium hydroxide that reacts with acetic acid in vinegar.
• Repeat the above procedure two more times to determine an accurate titer volume. Record the values in the table below.
• Dispose of the remaining chemicals and clean all the apparatus used.

Results

Titre	I	II	III
Final burette reading (mL)	8.7	8.8	8.7
Initial burette reading (mL)	0.0	0.0	0.0
Volume of NaOH used (mL)	8.7	8.8	8.7

 

The titer values representing the volume of sodium hydroxide used to neutralize acetic acid completely should be consistent and recorded to one decimal place. The principal of averaging should be applied to obtain the average titer volume.

     Calculation

Molarity of Acetic Acid (HCOOCH₃)

Average volume of sodium hydroxide = cm³

Moles of sodium hydroxide used

From the equation for reaction between sodium hydroxide and acetic acid:

NaOH _(aq)  + HCOOCH_{3 (aq)}   HCOONa _(aq)  + H₂O_(l)

Mole ratio

NaOH : HCOOCH₃ = 1 : 1

Moles of acetic acid = 0.004365 moles

acid (HCOOCH₃)

Mass percent

Mass of acetic acid = moles of acetic acid used x molar mass

= 0.004365 x 60.05

= 0.2621 grams of acetic acid

Mass of vinegar = volume x density of water

= 5 mL x 1 g/mL

= 5 grams

Mass percent =

Discussion

The mass percentage of acetic acid was calculated by determining the concentration and density of vinegar solution. The density of a vinegar solution was assumed to be the same as the density of water, which is 1 g/ mL. The mass percentage of acetic acid in vinegar was determined by expressing the mass of acetic acid as a ration of the total mass and representing it as a percentage. The experimental values of molarity and mass percent of acetic acid in vinegar were not the same as the theoretical values from preparation. The disparity might be as a result of experimental uncertainties such as inaccurate recording of the titer values. Moreover, some of the apparatus used in the experiment may have been faulty, leading to increased or lowered experimental values. The assumption made in the experiment is also not true since the water and vinegar solution does not have the same density. Therefore, the accuracy of the mass percent is lowered. Nevertheless, the experiment was a success since the variation in values was within the expected margins.

Conclusion

Acetic acid is a weak acid, whereas sodium hydroxide is a strong base. Sodium hydroxide quickly neutralizes acetic acid in a reaction that leads to the formation of salt and water as the only products. Qualitative analysis of acetic acid can be computed if the reactant is a standard solution. Therefore, the titration process is the best way to qualitatively determine the analytes. However, the accuracy of the experimental values can be improved by reducing errors.

Pre-Lab Answers

1. The endpoint in titration indicates complete reaction and is accompanied by the change of color by the indicator. Equivalence point refers to the point in a chemical reaction when only salt and water are produced. Equivalence point can also be termed as neutralization point.
2. An indicator in a chemical reaction is used to determine the endpoint or equivalence point of the reaction.
3. During the titration, a burette is set up and a 100 mL beaker placed under it. 10 mL of 0.50 M NaOH is placed in the burette, and 5 mL of vinegar is measured into the beaker.
4. When using a burette, it is important to record both initial and final readings of the burette to determine the volume of 0.50 M NaOH used. The titer volume is determined by analyzing the difference between the final burette reading and the initial burette reading. (volume of NaOH = final burette reading – initial burette reading).

Post- Lab Answer

Brand – Balsamic Vinegar of Modena

8,5 Fl. Oz. – Acidity- 6%

The analyzed percentage of acetic acid (5.242%) is almost the same as the theoretical percentage of acetic acid in Balsamic Vinegar of Modena (6%)

Results and discussion

1. The main objective of the experiment was to determine the percentage by mass of acetic acid in the vinegar solution by using the titration method.
2. To achieve this, a measured volume of unknown vinegar was titrated against a standard sodium hydroxide solution to determine the amount that completely reacts with the base. The mass used was expressed as a percentage of the total mass.
3. The experimental percentage of acetic acid was different from the theoretical one. This might be a result of uncertainties in the determination of the titration’s endpoint leading to inconsistent titer volumes. Besides, the assumption made on the density of vinegar is not accurate, leading to the errors.